at 68years old  Audio fever is on the rise again  my 1990 system  in part in need of a up grade  Starting with mp PLINIUS 16 PreAmp  with  a great phono stage Is being Replaced  with a  NAT Symmetrical  Balanced Tube PreAmp  Any Thoughts  @nd up Grade  Thiel 3.6  Speakers  for a pair of B &  W805-D3  Due To smaller living space  Driven By a KRELL  KSA 150 powerAmp can get some Advise  
Nice equipment & speakers. Have you thought about adding a couple subs & room treatment? 
Sounds like first rate upgrades. The NAT sounds like a good choice (I read a review)… the 805’s should be a great upgrade to the Thiels. Yes, a couple little subs would really round it out well. We have 5 x 805’s + 2 800 series subs for our home theater. They are great little speakers.
By all indications the NAT Symmetrical Balanced preamplifier is exceptionally good sounding.  Congratulations and I  believe that youll be very happy with It.
Thank You Thank You For all the good advise  YES  I Didn't incloud the rest of my Sys  A VPI CLASIC T/T With the HEAVY 20lbs SoundSmith The VOICE Cart  , REL Strada  III  Sub Parasound Jc3+ phono preamp Synergistic  Teslar  XLR Amp to PreAmp Two Richard very power conditioner Going into a Shyanta cloy cops Power  A VOODOO  Diamond power cable & Bogdan Spkr Cablkes  SND Pair os  Usher Compass Monitor Speakers  hifi Man EF^ Headpone Amp  AUDEZE Lcd3 Headphones Lots Of Extra cables i need to sell cheap  haven't figured out that part but than you 1 &  All for your advise greg 
That is some nice stuff there. Put the speakers on Townshend Podiums, put the VPI on Townshend Platform, and everything else on Pods. You will not believe the improvement.

Then get some TA-102 fO.Q tape. Cut a piece to fit between the cart and headshell. Put another thin strip down the underside of the tone arm. Put the rest anywhere else you like. Terrific stuff. Highly effective. Put Synergistic PHT (Black and Green) on the cart, and HFT on the speakers. Get Synergistic or AudioQuest or Cable Elevators or whatever ones you like, just get em, and get your cables up off the floor.    

Not just speaker. All your cables.  

For the subs you can save some money using Nobsound springs instead of Pods. But do get a couple more subs, as many as you can afford, to get to at least four. This will be another shocker.

Do all these, you will not believe. Very likely your system will sound better like this than anything you have heard anywhere at any price. But if not no worries, we haven’t even pulled out the big guns yet. I can hook you up. But first things first.
I've yet to hear a pre-amp (or amp) that bests the Convergent SL-1.  Have you heard one or given it any thought?
I Will  Try   The   TA-102 FO.Q  Tape i wonder if two many Tweks  gets  a little out of hand  with a reverse effect  
if you value the time, phase and coherent launch in your current speakers, you should give the Vandersteen Treo CT a listen. 

of course, you know what you are replacing is legend.

have fun….
Have to actually agree with Millercarbon (for once) about isolating speakers. I have B&W 805 D3 speakers, recently placed on IsoAcoustic Gaii's. Transformative sound. In fact the single biggest improvement made so far in my system.
Imagine if you had put them on Podiums! Not just speakers either. Speakers are obvious because they vibrate the most. But every component benefits. If the OP does his whole system then like I said the improvement will be hard to believe.